Partial demolition - Leave the basement intact?

Dear forum,

In a "densely populated" corner of Westphalia, we want to buy a home. Because the available building plots on site are usually too small, there is much to be said for buying a house.

Among other things, we have also set our sights on a plot of land on which there is already a detached single-family house (with an additional extension) with a granny flat and a triple garage. However, the condition and layout of the property are extremely poor, so because of the beautiful plot, we are considering partially demolishing the house.

I call my forum post partial demolition because the basement and the granny flat are supposed to remain. Is that "structurally" possible?

Is it even worth leaving the basement standing (technical [pipes and lines, possibly old or defective seals and insulation] and architectural [basement entrance] ties to the conditions)?

Hello,

Among other things, we have also set our sights on a plot of land on which there is already a detached single-family house (with an additional annex or extension) with a granny flat and a triple garage. However, the condition and layout of the property are extremely poor, so we are considering partially demolishing the house because of the beautiful plot.

I call my forum post partial demolition because the basement and the granny flat are supposed to remain. Is that "structurally" possible?

Initially, everything is possible; it is primarily a matter of structural engineering and, above all, the budget. I have implemented this twice so far and – one thing in advance with a request for consideration: Such a renovation measure cannot be done by just anyone, certainly not by a general contractor whose classic business is new single-family home construction. There are specialists for this, and they should be commissioned if you want to enjoy your own home in the coming years.

Is it even worth keeping the basement (technical [pipes and lines, possibly old or defective seals and insulation] and architectural [basement access] ties to the conditions)?

First of all, it needs to be clarified how old the masonry is – is there still usable structural data? If not, a structural engineer must first inspect the building and its substance on site. Afterwards, the contractor you trust, in cooperation with his/your architect, should draft the appropriate plans and calculate costs including demolition and possibly supporting measures. Not to forget, the disproportionately high demolition costs for the partial demolition.

Whether this construction project is worthwhile, I cannot answer reliably from my side of the computer since I neither know the building substance nor other parameters. Just this much: unless it is a historically valuable vaulted basement (and even that is usually an expensive hobby), I would always recommend a complete demolition. First, it is cheaper – no complex support measures have to be considered. Second, if current standards/technology are installed above the existing basement, it makes no sense to put this on outdated building fabric. And third – as long as it is not asbestos and the soil conditions allow it, the demolition material can be used for the floor construction; more or less material depending on whether new construction with or without a basement is planned.

Kind regards

Dear construction expert,

thank you very much for your reply.

what is a GU???

If I understand you correctly, you are advising against it not only for economic reasons but also because of the collaboration between different trades that would be required due to the "Keller-Problematik"?!?! As background to our "plans":

We have considered a version without a basement, which is how we came to the thoughts described. However, your explanations are understandable.

If you already have experience with demolition, how should one proceed? Does the determination of any arising "Sondermüll" take place by an appropriate demolition company, or is a specialist required here? Are there interfaces between the provider of the prefab house and the demolition? And does it make sense, from the perspective that I will probably still need a slab (and furthermore the construction group will have to be backfilled in the case without a basement), to put all the "preparatory work" into the hands of an architect who handles all the services bundled from a single source???

Thank you for your answers!
zicoandenball

Hello,

what is a GU???

GeneralContractor

If I understand you correctly, you advise against it not only for economic reasons but also because of the cooperation between different trades that would be required due to the "basement issue"!?!?!

In my experience, such a project can only succeed if people involved in the realization specialize exactly in these tasks; everything else is Russian roulette.

We have considered this option. It has no basement, which is why we came up with the described idea. Your explanations, however, are understandable.

One more thing from my experience: with a prefab house provider, the basements often only fit where they also arranged the suppliers for the basement

If you already have experience with demolition, how would you proceed then?

In case of partial demolition: first request the structural analysis or have it newly created if necessary; commission a soil surveyor. Then, as a rule, the structural engineer and the builder you trust meet at the site. All three will then be able to answer all your questions regarding possible hazardous waste, soil conditions, and costs.
In case of complete demolition, order a soil survey and then commission a demolition contractor of your choice with an offer.

Are there interfaces between the prefab house provider and the demolition?

Only if you choose the partial demolition option.

And, considering that I will probably still need a foundation slab (and that the construction group must be filled again if there is no basement), does it make sense to put all the "preparatory work" in the hands of an architect who bundles all services from a single source???

Regarding partial demolition, I already answered you.

If you have a complete demolition done, the prefab house provider should be able to initiate the necessary steps on your behalf in close coordination with the involved trades. Otherwise, this statement “uour architects turn your dreams and ideas into a unique piece - state-of-the-art manufacturing technology, qualified specialists and selected ecological building materials make a masterpiece out of it” wouldn’t be worth the paper it’s printed on.

Kind regards